Rare earth elements abound in, and account for around 0.0153% of the mass of, the crust of the Earth. The density of distribution of rare earth elements in the crust of the Earth is much lower than that of common metals, such as zinc, tin, and cobalt. Among rare earth elements, cerium has the largest density (0.0046%) of distribution in the crust of the Earth, then come yttrium, neodymium, and lanthanum. Rare earth elements mostly feature an enrichment ratio of less than 1%, though some feature a maximum enrichment ratio of 4% to 9%. Therefore, rare earth mining incurs very high costs, not to mention that it is extremely difficult to separate and produce highly pure rare earth elements. Hence, rare earth mining will not be cost-effective, unless the products thereof are sold at high prices. Rare earth metals are required for the manufacturing of necessities, such as vehicle catalyst adapters, catalysts for use in petroleum refinery, magnetic materials for use with permanent magnetic motors, thunderbolts for use in a cigarette lighter, glass, and dyes for use with porcelains, as well as indispensable additives for use in processes carried out in high-tech industries, such as aerospace industry, electronic industry, laser-related industry, nuclear power generation, and superconductor-related industry. When used in metallurgy, rare earth metals enhance the performance of the alloys of steel, aluminum, magnesium and titanium. Although global annual revenues derived from transactions of rare earth metals nowadays total to billions of U.S. Dollars, rare earth metals are indispensable to high-tech industries. Rare earth metals are regarded as military tactical resources by major industrialized countries around the world. Therefore, rare earth materials are dubbed “industrial vitamins,” “Mother of new materials” and “Gold in the 21st century,” and the rare earth industry is referred to as a “rising industry.”